Radome deicing by infra-red focused via parabolic reflector through waveguide onto window



March 9, 1965 D. F. BOWMAN 3,173,141

RADOME DEICING BY INFRA-RED FOCUSED VIA PARABOLIC REFLECTOR THROUGH WAVEGUIDE ONTO WINDOW Filed May 8, 1962 INVENTOR @4100 50WM/M/ a," 0 BY United States Patent 3,173,141 RADOME DEICING BY INFRA-RED FOCUSEI) WA PARABOLIC REFLECTGR THRUUGH WAVE- GUIDE ONTG WINDOW David F. Bowman, Wayne, Pm, assignor to I-T-E (Iircuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed May 8, 1962, Ser. No. 193,664 3 (Ilaims. (Cl. 343-704) This invention relates to a surface heating system and more particularly to a radome deicing system, wherein a concentrated beam of heat energy is introduced into the R-F horn in a manner that will minimize interference with the propagated electro-magnetic energy.

In many antenna systems operating in frigid climates, a continual accumulation of ice tends to form on the radome. This interferes with signal propagation and presents several maintenance and structural problems to the antenna structure. Accordingly, it is necessary to provide for the deicing of such radome structures, and numerous systems are presently known to introduce a source of heat to the radome structure to effect deicing.

One such arrangement is to imbed heater Wires in the radome structure itself. However, the orientation of the wires severely limits the transmission of electro-magnetic energy through the radome.

Another arrangement is to include a heater and blower system to force warmed air through the horn structure and onto the radome surface. This arrangement presents serious maintenance and reliability problems.

Still another arrangement is to include a perforated metal plate at the side walls of the horn structure and to present this plate to a source of infra-red energy. Because of the relatively inefficient and poor transmissivity of perforated metal Walls to infra-red energy impinging at Oblique angles, this system requires excessively large infra-red sources to effect a substantial amount of heat transfer. This system will also increase the blocking area of the horn, and therefore have a deleterious effect upon the transmission of the electro-magnetic wave energy therethrough.

My invention permits deicing of the radome structure in a preferred manner which presents negligible interference to the electro-magnetic wave channels, requires a minimum of maintenance and may readily be added to or removed from an existing antenna system.

Briefly stated, my invention introduces a concentrated beam of heat energy, preferably infra-red energy, into a small aperture located in the R-F shadow of the horn. This small aperture is preferably contained in a waveguide bend or mitered elbow which is constructed to be readily attached to the throat of an existing horn structure. This aperture-containing Waveguide joint is adapted to be affixed to the heat introduction assembly, which is so orientated with respect to the aperture as to present a concentrated beam of energy thereto thereby permitting a minimum size aperture opening.

In the illustrative embodiments of my invention the heat introduction assembly includes a parabolic reflecting surface and a source of infra-red energy located along a plane parallel to the focal plane thereof. The reflecting surface is enclosed by a protective housing. Both the reflecting surface and the housing are preferably constructed of a material which acts as a good reflector of infra-red energy (e.g. aluminum). The aperture opening is located at the focus of the parabolic surface. By virtue of the well-known mathematical properties of a parabolic surface, the source of energy will be reflected and concentrated into a beam at the focus located aperture.

This beam of energy enters the small aperture of the waveguide joint and is guided down the horn. The in- "ice terior horn walls are also preferably constructed of aluminum for good infra-red reflection. The infra-red energy will strike the radome surface at a small angle of incidence, and therefore effect appreciable heat transfer. Inasmuch as the infra-red energy will be striking the horn walls at a much greater angle of incidence prior to reaching the radome structure, little of its energy will be dissipated therein and the temperature of the horn will preferably be kept lower than the radome. The maintenance of such a lower temperature is desirable from the standpoint of efliciency, safety, and increased life of the horn because of the reduction of thermal expansion caused warpage.

In one embodiment of my invention a line source of infra-red energy is longitudinally disposed in a plane parallel to the focal plane of a parabolic semi-cylinder and perpendicular to the principal axis thereof. Preferably, an additional planar reflecting surface is disposed in another plane parallel to the source plane and more remote from the parabolic reflecting surface to provide increased reflections from the infra-red source. The aperture opening of the waveguide joint is flange-adapted to be fastened to a mating opening located at the focal plane of the parabolic reflecting surface.

In a modified embodiment of my invention, planar sources of infra-red energy are disposed in a plane parallel to the focal plane of the reflecting surface, which may be either a parabolic cylinder or paraboloid of revolution. An opening located at the focus of the reflecting surface is flange-adapted to be fastened to the waveguide joint.

It is thus seen that my invention permits an existing antenna system to be readily modified for the inclusion or removal of the deicing feature by the mere substitution of an appropriate waveguide joint. The basic concept of my invention resides in the introduction of a concentrated beam of infra-red energy into a small aperture of a waveguide joint located in the R-F shadow of the antenna horn; with the aperture opening being located at the focus of a parabolic reflecting surface which produces the aforesaid concentrated beam of infra-red energy.

It is accordingly a primary object of this invention to provide a radome deicing means which presents a minimum degree of degradation to the electro-magnetic wave energy channels.

Another object of this invention is to provide a radome deicing system of a simplified construction to present a minimum amount of maintenance and reliability problems to an antenna system.

A further object of this invention is to provide a radome deicing system which may readily be added to an existing antenna system as an optional feature thereof.

An additional object of this invention is to provide a radome system wherein a concentrated beam of heat energy is introduced into a relatively small aperture located in the R-F shadow of the antenna horn.

Still another object of this invention is to provide a radome deicing system wherein a source of infra-red energy is disposed in a plane parallel to the focal plane of a parabolic reflecting surface, and a relatively small aperture is located at the focus thereof to introduce the infra-red energy to the antenna system.

Still a further object of this invention is to present a concentrated beam of infra-red energy to the rear of an antenna horn by means of a small aperture located at the focus of a parabolic reflecting surface, said parabolic reflecting surface having a source of infra-red energy disposed in a plane parallel to the focal plane thereof.

These as well as other objects of my invention will readily ecome apparent after reading the following description of the accompanying drawings in which:

FIGURE 1 is a perspective view of a preferred embodiment of my invention, showing a line source of infrared energy and a semi-cylindrical parabolic reflecting surface.

FIGURE 2 is a cross-sectional view of FIGURE 1 along line 2.2 and looking in the direction of the arrows, illustrating the orientation of the parabolic reflecting surface, infra-red source and horn aperture opening.

FIGURE 3 is a schematic cross-sectional View of a second preferred embodiment of my invention utilizing a plane source of infra-red energy.

FIGURE 4 is a simplified illustration of the beam concentrating concept of the parabolic reflecting surface utilized in my invention' Referring initially to FIGURE 1, radome is located at the aperture end 11 of horn 20. Horn 219 may typically.

be constructed in the manner set forth in my copending U.S. Patent application (A-l08) Serial No. 166,205 filed January 15, 1962, entitled Microwave Signal Transfer Apparatus, 'asigned-to the assignee of the instant invention, wherein two orthogonally related signals are introduced thereto via waveguides 21 and 22 and combined by spear 23. Radome 10will tend to have an ice formation, typically shown as 12 on its outer surface, caused by the climatic conditions to which it is subjected. The purpose of this invention is to introduce a source of heat energy against radome 11 to melt or deice its structure.

Heat source assembly includes a source of energy 31 locatedin a plane parallel to the focal plane 32 of parabolic reflecting surface 33. Heat source 31 is typically shown as a line source of infra-red energy, withit being understood that other heat sources may be used without departing from the inventive concept of my system. Theheat energy source is preferably enclosed by side surfaces 34, 35; bottom surface 36; and front surface 37 to provide environmental protection. An aperture opening 38 is located in front surface 37 at the focus of elliptical reflecting surface'33. Front surface 37 will preferably be a planar reflecting surface disposed in a plane parallel to the local plane of the elliptical surface to thereby increase the reflective energy impinging on parabolic surface 33. The inner surfaces of housing members 34-37 are constructed of a material which serves as a good reflector of infra-red energy (eg. aluminum) to maximize the portion of the energy emanating from source 317which strikes surface 33. An additional planar reflecting surface 39-may be provided to further increase the reflective energy. As will be shown below in conjunction with the discussion of FIGURE 4, the infra-red energy emanating at source 31 will strike parabolic reflecting surface 33 and be reflected as a beam of energy concentrated at the focus 38 thereof.

A thermostatic control system, schematically shown as box 46, with an externally accessible dial 41, is preferably included to permit adjustment of the deicing functions in accordance with the existing climatic conditions. Thermostatic control-40 is connected via wire 42 to an appropriate source of power to energize infra-red source 31. Wire 43-connects thermostatic control 40 to infrared source 31.

Front surface 37 includes flange 44 about focus opening 38 to interconnect to flange 45 of waveguide joint section 50. Waveguide joint section is flange adapted at 46 to interconnect to horn 24 via waveguide section 22. A small opening 38a in waveguide joint 50 mates with focus opening 38 to permit the introduction of the concentrated beam of infra-red energy into waveguide section 50. Waveguide joint 50' may typically be a conventional Waveguide bend or m-itered elbow which is adapted to be. readily interconnected or removed from horn vstructure 20; It is thus seen that the heat source assembly of my invention is constructed to be readily added to or removed from the existing antenna system to provide for optional deicing where necessary.

The concentrated beam of infra-red energy entering aperture opening 38a will be spread out and strike inner surfaces of waveguide 22 and horn 20 at large angles of incidence as it is guided by the multi-reflections down horn 20 to aperture opening 11. The infra-red energy will then strike radome 10 at a small angle of incidence so as to effect considerable heat transfer thereto. Horn 21?,waveguide 22 and joint 5i) are preferably constructed of aluminum for good'infra-red reflection.

. Referring now to FIGURE 4, which illustrates the beam concentrating properties of my invention, infra-red source 31 is located'in focal plane 32. Alternatively, source 31 may be located in other planes parallel to the focal-plane of parabolic surface 33. Source 31 generates a-plane wave of energy which impinges reflecting surface 33, and by the Well-known properties of a parabola will be concentrated into a beam of energy at the focus 38 thereof; focus 38 being located 'at the intersection of focal plane 32 and principal axis 39.

Reference is now made to FIGURE 3, which schematically illustrates a somewhat modified embodiment of my invention which utilizes planar sources 31 and 31" of infra-red energy. The planar emanating surface thereof is preferably shown located in the focal plane 32 of parabolic surface 33, which may be a parabolic cylinder or paraboloid of revolution. Aperture opening 38a of Wave guide joint 5i) located at the focus of surface 33' permits the introduction of a concentrated beam of infra-red energy to horn 2! in the manner set forth above in conjunction with FIGURES 1 and 2, wherein it is guided towards radome 10.

Numerous other embodiments may be constructed using one or more linear or planar sources of infra-red energy arranged in accordance with the teachings of FIG- URES 1 or 3. It is therefore seen that I have provided an improved radome deicing system, whereby a concentrated beam of heat energy, preferably infra-red, is introduced into a small aperture opening in the 'R-F shadow of the antenna horn and is transmitted therethrough wherein it strikes the radome at an angle which effects substantial heat transfer thereto.

A practical working embodiment of my invention can typically be constructed to operate in conjunction with a troposcatter communication system, utilizing commercially available WR 975 Waveguides operating in the 755-935 megacycle band. Such a working embodiment would present a negligible increase in Standing Wave Ratio, or reduction in Interchannel Isolation in comparison to the same troposcatter system before the addition of the optional deicing feature. However, should the increase in Standing Wave Ratio be measurable, it may be matched out by fixed compensation elements, the design of which is well known to the art.

In the foregoing disclosure thisinvention has been described With'preferred illustrative embodiments. Since many variations and modifications will now become apparent to those skilled in the art, I prefer therefore not to be limited tothe specific description contained herein, but only by the appendedclaims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows.

What I claim is:

1. An antenna radome deicing system, wherein said radome is located at the front of ahorn structure and electromagnetic wave channel means couples to the rear of said horn structure for forwardly coupling electromagnetic wave energy towards said radome; said system comprising a heat energy source and a beam concentrating means as-' 'said heat energy beam and the electromagnetic wave energy associated with said electromagnetic wave channel means, whereby said heat energy and said electromagnetic energy is forwardly guided towards said radome, said aperture directing said heat energy into said horn structure to forwardly travel towards said radome while striking the inner walls of said horn structure at a large angle of incidence, and terminating against said radome at a small angle of incidence.

2. An antenna radome deicing system, wherein said radome is located at the front of a horn structure and electromagnetic wave channel means couples to the rear of said horn structure for forwardly coupling electromagnetic wave energy towards said radome; said system comprising a heat energy source and a beam concentrating means associated therewith; a hollowed guide member positioned behind said horn, and in the R-F shadow of said electromagnetic wave energy; means for connecting said hollowed guide member to said electromagnetic Wave channel means; an aperture substantially smaller than said heat energy source located in said hollowed guide member; said aperture being operatively positioned to receive said concentrating heat energy beam and present said beam to said horn; said horn being a common guide for said heat energy beam and the electro magnetic wave energy associated with said electromagnetic wave channel means, whereby said heat energy and said electromagnetic energy is forwardly guided towards said radome, said aperture directing said heat energy into said horn structure to forwardly travel towards said radome while striking the inner walls of said horn structure at a large angle of incidence, and terminating against said radome at a small angle of incidence, said beam concentrating means is a parabolic reflecting surface and Said heat energy source supplies infra-red radiation, and is positioned in a plane parallel to the focal plane of said parabolic surface; and said aperture is located at the focus of said parabolic surface.

3. An antenna radome deicing system as set forth in claim 1 wherein said connecting means comprise a pair of complementary flanges; a first of said flanges secured to the rear end of said wave channel means, and a second of said flanges secured to the forward end of said hollowed guide member; said flanges when connected, comprising aligned first and second control openings defining said aperture for introducing said heat energy into the rear of said electromagnetic wave channel means.

References Cited by the Examiner UNITED STATES PATENTS 3,080,483 3/63 Jatfe et al. 219-34 HERMAN KARL SAALBACH, Primary Examiner. 

1. AN ANTENNA RADOME DEICING SYSTEM, WHEREIN SAID RADOME IS LOCATED AT THE FRONT OF A HORN STRUCTURE AND ELECTROMAGNETIC WAVE CHANNEL MEANS COUPLES TO THE REAR OF SAID HORN STRUCTURE FOR FORWARDLY COUPLING ELECTROMAGNETIC WAVE ENERGY TOWARDS SAID RADOME; SAIS SYSTEM COMPRISING A HEAT ENERGY SOURCE AND A BEAM CONCENTRATING MEANS ASSOCIATED THEREWITH; A HOLLOWED GUIDE MEMBER POSITIONED BEHIND SAID HORN, AND IN THE R-F SHADOW OF SAID ELECTROMAGNETIC WAVE ENERGY; MEANS FOR CONNECTING SAID HOLLOWED GUIDE MEMBER TO SAID ELECTROMAGNETIC WAVE CHANNEL MEANS; AN APERTURE SUBSTANTIALLY SMALLER THAN SAID HEAT ENERGY SOURCE LOCATED IN SAID HOLLOWED GUIDE MEMBER; SAID APERTURE BEING OPERATIVELY POSITIONED TO RECEIVE SAID CONCENTRATING HEAT ENERGY BEAM AND PRESENT SAID BEAM TO SAID HORN; SAID HORN BEING A COMMON GUIDE FOR SAID HEAT ENERGY BEAM AND THE ELECTROMAGNETIC WAVE ENERGY ASSOCIATED WITH SAID ELECTROMAGNETIC WAVE CHANNEL MEANS, WHEREBY SAID HEAT ENERGY AND SAID ELECTROMAGNETIC ENERGY IS FORWARDLY GUIDED TOWARDS SAID RADOME, SAID APERTURE DIRECTLY SAID HEAT ENERGY INTO SAID HORN STRUCTURE TO FORWARDLY TRAVEL TOWARDS SAID RADOME WHILE STRIKING THE INNER WALLS OF SAID HORN STRUCTURE AT A LARGE ANGLE OF INCIDENCE, AND TERMINATING AGAINST SAID RADOME AT A SMALL ANGLE OF INCIDENCE. 